c# - 任务 FromResult 与 TaskCompletionSource SetResult

Question

关于的功能和含义有什么区别

TaskCompletionSource + SetResult vs Task + FromResult

在 SendAsync 方法中？

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    if (request.RequestUri.Scheme != Uri.UriSchemeHttps)
    {
        var response = new HttpResponseMessage(HttpStatusCode.Forbidden) {ReasonPhrase = "HTTPS Required"};
        var taskCompletionSource = new TaskCompletionSource<HttpResponseMessage>();
        taskCompletionSource.SetResult(response);
        return taskCompletionSource.Task;
    }
    return base.SendAsync(request, cancellationToken);
}

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    if (!request.RequestUri.Scheme.Equals(Uri.UriSchemeHttps, StringComparison.OrdinalIgnoreCase))
    {
        HttpResponseMessage reply = request.CreateErrorResponse(HttpStatusCode.BadRequest, "HTTPS is required for security reason.");
        return Task.FromResult(reply);
    }

    return base.SendAsync(request, cancellationToken);
}

Answer 1

Task.FromResult 是 .NET 4.5 中的新增功能。它是创建 TaskCompletionSource 并调用 SetResult 的辅助方法。如果您使用的是 .NET 4 或更早版本，则必须使用 SetResult。